This invention is used on the one hand in the realization of the coupling between conventional optical fibers and integrated circuits for detection or emission of radiation, and on the other hand in the field of optical connections in micro-opto-electronics.
Such a device is known from the publication of F. J. Leonberger et al. in Applied Physics Letters 38 (5) of March 1, 1981, pages 313-315, entitled "Low loss GaAs optical wave guides formed by lateral epitaxial growth over oxide". This document discloses a method of manufacturing wave guides on a monocrystalline substrate of gallium arsenide covered with a layer of silicon oxide (SiO.sub.2). Windows are opened in this layer by etching, and an n.sup.+ doped monocrystalline gallium arsenide layer is formed in these windows by epitaxial growth. At the beginning of the growing process, the layer of n.sup.+ GaAs is formed from the starting material constituted by the substrate exposed in the opening of the windows, after which, when the epitaxial layer thickens, it reaches the sides of the windows and finally forms above the whole layer of SiO.sub.2 a uniform layer of monocrystalline n.sup.+ doped GaAs. After this layer of GaAs has been formed, the wave guides are formed by etching this layer. These wave guides have the form of a ribbon of rectangular section. Due to the underlying layer of silicon oxide the losses along a guide of this type are rather low and the attenuation along such a wave guide is of the order of 2.3 dB/cm at a wavelength of 1.06 .mu.m.
However, the light propagated in such a guide is poorly confined by the lateral walls. In fact, since these guides are etched in the layer of gallium arsenide not as deep as the layer of silica (SiO.sub.2), they do not exhibit interfaces between air and gallium arsenide (GaAs) over the whole height of the lateral vertical surfaces, but only over part thereof. Now, if the interface between air and gallium arsenide (GaAs) permits on the upper surface of the guide of obtaining a very high total reflection due to the difference in refractive index between air and gallium arsenide (GaAs) of .DELTA.n.perspectiveto.2.5, on the contrary, the fact that there is no interface between the guide and the continuous layer of gallium arsenide (GaAs), involves losses along the longitudinal walls of the guide. On the other hand, the lateral and upper walls obtained by the chemical etching treatment have a rough surface. This surface state also gives rise to losses.
These losses are even more strongly pronounced when the guide should be given a radius of curvature to incurve the path of the light.
For the envisaged applications, the technical problem arising is to provide a device so that both ultrahigh speed integrated circuits can be realized and the light can be propagated with a low attenuation. Investigations have shown that the ideal attenuation must not exceed 1 dB/cm for a wavelength of 1.06 .mu.m.
The device proposed in the aforementioned publication, which has an attenuation of 2.3 dB/cm in this wavelength range, cannot be utilized to form wave guides of great length. Moreover, since the light is poorly confined along the longitudinal walls, this device cannot be utilized to form wave guides having small radii of curvature.